Prepare for release.
* maint.mk (alpha): Check for PREV_VERSION setting sooner, and
remove tag operation.
(version-check): Enhance this check.
(prev-tarball): Depend on version-check.
(this-vc-tag): Delete, and mention need to run tag...
* HACKING: ...here, prior to make maintainer-distcheck.
Update the instructions to match this particular release process.
* Makefile.am (.version, announcement): Allow for VPATH build.
* cfg.mk (gnulib_dir): Likewise.
* doc/Makefile.am ($(srcdir)/m4.1): Include release number in man
page.
Signed-off-by: Eric Blake <ebb9@byu.net>